Telephone system



Nov.28,-1944. A, HUBBARD 2,363,671

TELEPHONE SYSTEM Filed Dec. 51, 1942 5 Sheets-Sheet l HWEA/TO/ F. A.HUBBARD A T TOD/VF V Nov. 28, 1944. F. A. HUBBARD 23,353,671

' TELEPHONE SYSTEM J Filed pee. 31, 1942 5 Shets-Sheet 2 MAI/EN TOR F A.HUBBARD ATTORNEY I Nov. 28, 1944. U BARD 2,363,671

TELEPHGNE SYSTEM Filed Dec. 31, 1942 5 Sheets-Sheet 4 F/GJO was /00INVEN 70/? F. A. HUBBARD A TTOR/VFV I Patented Nov. 28,1944

r 2,363,671 TELEPHONE SYSTEM Francis A. Hubbard, Maplewood, N.J.,a.ssignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporationof New York Application December 31, 1942, Serial No.470,724. to

o e o 14 Claims. l 'I' his invention relates to signaling andcommunication systems. and particularly to telephone systems in whichautomatic switches used in the establishment of telephone connectionsare controlled by means of alternating current.

Systems have been proposed, heretofore in which the designationsofcalled: lines are transthe first or the second of the three condensersmitted from one pointft'o anotherby'means of alternating "currents "ofdifferent frequencies transmitted singly or in combinationcharacterizing the different digits or other characters of a wanted linedesignation. In Patent No. 2,164,- 335, is'suedJuly 4; 1939, to R. C.Mathes,.there is disclosed a system of this general character in which aharmonic generator is employed at the In the proposedtransmittera}resonant sup pression circuit is provided comprising two don-Q ble'wound retard coils each having its windings connected in seriesopposition and three fcondensers. One coil may be tuned to either of twofrequencies a or b by the connection of either to the mid-point betweenthe windings by the operation of a first or second switch element, andthe second coil may. be tuned to the frequency 0 by the connection ofathird condenser to the mid-point between its windingsby the operationof a third switch element. Preferably the switch elements are of thetimed mercuryjcontact type subscribers station which is activated byourrent of a fundamental frequency generated at the central ofiicetoproduce .harmonicsof this fundamental frequencyand in which thesubscriber l is" provided with means. for selecting certain of r thegenerated harmonics to characterizethe digits of a telephone designationand to cause the selected harmonics tobe.suppressed to. control theoperation of automaticfswitches. A further improvement on the: systemdisclosed in the patent to Mathes just referred tois disclosed in PatentN0. 2,201,296issued May 21, .1940, to A. A.

Lundstrom and E. L. Norton.

It isthe' object of the presentinvention to further improve systems ofthis type. whereby a smaller number of generated harmonics are utilizedto characterize the digits. of a telephone designation.

and are selectivelyoperable once during the down-stroke of a key-setkeyand are selectively operable again during" the up or return strokeoflan operated keyin accordancewitha predeterminedcode; v. v v r A codemay be so selected with respect to the standard arrangement of thekeysin the keysetas indicated. in a table appearing hereinafter that everykey suppresses a single harmonicron the down-stroke. and. that no. two,adjacent keys arranged either vertically or horizontally sup press thesame harmonic onthe down-stroke. wIl'l accordance with the-code all.keys but theukey for the digit ,0 suppresses a singleharmonic on i l itsup-stroke, the keyforthe digit O suppressing "It is a further object of.the present invention to enable a wider spacing of the utilizedharmonics iwithout increasing the outside frequency rangewhereby agreater discrimination. by the receiving channels is secured or anarroweroutside frequencyrange of. the harmonicsmay be employed wherebythe difference in attenuation betweenthe highest and lowest frequenciesis In accordance,w ith one embodiment of themvention. these objects areattained by the provision of mechanism in a call transmitterof thegeneral type disclosed in the Patent No. 2315 344 granted March 30,1943, in the name of R. F. Mallina whereby the operation of any one ofthe ten; keys ofthe key-set is effective upon the down-stroke toselectively suppress one ofthe harmonics which characterizes the digitcorresponding to the depressed key andtagain upon the up-stroke of theoperated key to suppress one, or more harmonics which characterize thedigit .55

corresponding to the operatedjkey.

two harmonics simultaneously on its up-stroke.

The seriallyconnected suppressionfc-oils are connectable to the, tipconductor-of the .substation line through a fourth. condenser by anoffnormal switch of the timed mercury contact type. Thiscifi-normalswitch is momentarily operated during the down-stroke movement ofanygkey and is again momentarilypperated during the up-stroke movementof the operated key to transfer the substation line from the substationsubset to the harmonic generator coil of the. call j transmitter. Byconnecting this condenser in se ries withthe generator coilandsuppression coils, the off-normal switch when operated, opens the directcurrent path at the substation whereby central office equipment may besignaled and conditioned to receive voice frequency signals thus"eliminating certain 'difficulties that have heretofore appeared tobeinherent inthe sys temsof this type hereinbefore proposed, byentirelyseparating the signalingcondition from the normal talkingcondition, eliminatinginterference between the two and by providing apositionsignal to activate the receiving channel,

. The production of two signal impulse conditions by the calltransmitter foreach keyeddigit wwi sponse to the suppression of one ofthe three frequencies suppressed upon the down-strokeof an operated key,and the other group being associated with the three receiving channelsfollowing the termination of the first impuiseof .a digit sig-= ing 3 isattached. Secured to the base I is a mounting plate 4 having upturnedears 5 and 6 for supporting a shaft 1 on which the key member Kl toKill, inclusive, are pivotally mounted;

an upturned and then inturned bracket 8 upon which the off-normal switchassembly 9 and the suppression switch assembly I are secured by thescrews ll; an ear I2 for supporting one end of the pivot screw l3 uponwhich the armatures of the switch assemblies 9 and "1C are pivoted; anupturned and then inturned bracket l4 upon "which the suppression switchassemblies IDA and nal so that relays of such group are selectivelyoperablein response to the suppression of one 'or more of the threefrequencies upon the upstroke of the operated key. Thus upon the terurna ion of the wo impulses .of a digi nal a re ay. of the first .sreupandone or two rel ys of thel eccnd group w ll m in ope to 9 trol thesetting of a digit register of the sender. For a clearer understandingof the invention reference may be had to the following detailed descrption t ken in connection with the accompan in d awin s n Which;

Fig, 1 is a left side elevation view of the telephone call tfiansmitter' mbodying the invention, the casing being shown with aportion broken away to disclose the frequency suppression switches andthe key-controlled operating mechanism therefor;

,Fig. 21$ 3 top plan View of the callv transmitter with a portion of thecasing broken away;

Fig. 3 is a right side elevation view of the call transmitterthe casingbeing shown with-a portionbroken away to disclose one of the frequencysuppression switches and operating mechanism therefor Fig. is anenlarged side elevational detail view of the frequency suppressionswitch disclosed in Fig. 3; r

Fig. 5 is, an enlargedend view of an assemblage of'a suppression switchand the off-normal switch; I

s Fig. 6 is a detail View of the end of the operating levers associatedwith the suppression switch disclosed in Figs. 4 and 5; i

Fig. 7 is a detail view of the end of the offnormal switch operatinglever associated with the oiif-normal switch disclosed in Fig. 5;

Fig. ,8 is a detail view, partly in cross-section, of" one of themercury contact Switch elements a so i edw th h uppression switches andoff- ,swi c and i s-: l9 and 11,. taken together, show a tele phone systmin accordance with the pres t i vention. and in which. the calltransmitter dis-. lose in Fi s 1. t 8, inclusive, s empleyedz Fig. 9 .shwing the. substation. circuit in which the; call transmitter is,installed, a diagrammatic illn strationof allnefinder; first selector,a. sender link comprising a run fln erand sender selector and aportiqhof the, circuits of a; central office send F sshamin t e re ivinchannels of thesender, the; recording relays and other contror relaysand Fig. 1 1 showing certain of; the sender refisters; and progress;relays associated there.-

I 16- i tra mitter of the invention as shown; in. Figs; 1-, 2: and, 3, abase If? is provided" a n upturned edges 2 to which a molded casbracket.i For camm'ing the armature 36 away from the polar'ends of thepole-pieces 32 and 33, the ho-ri-q .lllB are secured by the screws l5;the ear I6 "for supporting one end of the pivot screw l1 upon 'wh'ichthe.armatures of the switch assemblies IBA and 1B are. pivoted; and anupturned plate Each of the key members Kl to KIU, inclusive,

is normally and yieldably maintained in the posiin differentcombinations upon the depression of the key'members. These bars arenormally and yieldably held in the positions disclosed in Fig. l byretractil-e springs 20 which are hooked at one of their ends to theupper edge of plate l8 and at their otherends are hooked to lugs 2| oflever members '22, 23, 24, 25, 26,-and 21 which are secured to theU-bars B1, B2, B3, B4, B5, and

B6, respectively as by rivets 28.

A U-shaped off-normal bar B1 is also pivoted on shaft 1 and held inoperable relation with each of the ten' key members K I to Kitinclusive, by a retractile spring 29 hooked at one of. its ends to alugon the lever 30 secured to the bar B! as by rivets 3| and at theother of its ,ends to the plate 18. control the off normal switchassembly 9 once when any key of the key-set is operated in a down-strokeand. again when the operated key is. released in an up-stroke.

The off-normal switch assembly 9 comprises two parallelly disposedpole-pieces 32' and 33 clamped by the clamping screws l I, previouslyreferred to, to the pole-pieces of. a permanent magnet 34 as bestshownin Fig. 3. The pole-pieces are provided near their outerends withaligned holes in which is supporteda switch element 35 of the mercurycontact type. A switchel'ement of this type is disclosed in Patent No.2,295,602, granted September '15, 1942, to C. E. Pollard, Jr;Cooperating with the polar ends of the pole pieces is a soft ironarmature 36. The armature is channel-shaped, theflanges 31 and 38thereof having aligned holes'therethrough near their lower ends throughwhich the pivot screw I3 extends and on which screwthe armature ispivoted} The inner end of the pivot screw is threaded inter 31 of thearmature 36 and at its other end tothe entension M of the bracket 8'which extens1on 1sbent inwardly at; right angles. to the zontal of lever30', which lever is secured. to

the off-'nonnal' bar'Bl, extends beneath the pole-I The lever 30 iseffective to ascac'zr piece 33 with its tip 42 engaged in the. opening43 in the armature 36 and abovethecamming mercury between the upperedges of the guide portion 44 thereof. The shape ofthis camming portionis best disclosed in connection with the armature 51 of the switchassembly IOC disclosed inFig. 4. When the end of the lever is depressedthe camming end of such lever en ges with the camming portion 44 of thearmature and cams the armature 36. away from the polar ends ofthepole-pieces 32 and 33, but when the end of lever 39 is fully depressed,inwhich position the camming end 42 thereof will be below thecam portion4440f the armature and within the opening 45 in the armature, the spring40 and the attractive force of the permanent magnet 34 will draw thearmature again into engagement with the polar ends of the pole-pieces.Similarly, in the return movement of the lever 30 when the depressedkey-set keylis released, the camming end 42 of such lever movingupwardly over the camming portion 44 of the armature again moves thearmature away from the pole-pieces until the timing end 42 reenters theopening 43 in the armature. 1

i The mercurycontact switch element 35 of the off-normal switchassembly, as bestdisclosed in i Fig. -8, is, as previously stated, ofthe type disclosed in the patent to Pollard hereinbefore referred to andhas an envelope 45 of glass or other suitable material within which is aguide sleeve '41 entirely open at its upper end and partially closed atits lower end to add rigidity thereto and supported on and secured tothe upper end of the terminal wire 48. The wire 48 is sealed through thebottom of the envelope 46. The guide sleeve 41 is made of a materialsuch as nickel which is wettable by mercury. Sealed through the upperend wall of the envelope are two parallelly disposed contact members 49and 5i] having their ends which extend into the envelope bent at rightanglestoward each other to form two stationary contact portions 5| and52,the upper one 52 of which serves as a front contact and the lower one5| of which serves. as a back contact. The contact portion 52 is widebut the contact portion 5| is narrow. Movable within the guide sleeve 41is a cylindrical tubular armature 53, the ends of which are entirelyopen. The armature ismade of magnetic materialbut its surfaces are suchthat they are readily wettable by mercury. Secured to the inner surfaceof the armature and movable therewith is a contact member 54 which maybe formed by doubling a length of wire, bending the looped end at rightangles and flattening the same to provide awidened contact portion 55 ifor engagement with the contact portions 5| and 52 of the back and frontcontact members 49 and 50. X A contact of this type has the property ofconducting mercury along the capillary' ducts formed therein to itsupper contact portion from which a small amounto-f mercury istransferred 4 to the surfaces of the contacts with which it cooperates.v To complete the switch element a measured amount of mercury56 isdepositedin the bottom of the envelope which envelope is then evacuated,refilled withta gas such as hydrogen to a required operating pressureand then sealed. The meronly in the envelope rises within the guidesleeve 41 and within the tubular armature 53 to the position illustratedin Fig. 8 and the mercury is also conducted by the capillary action ofthe inner surface of the guide sleeve 4'! and the outer surface of thearmature 53 to fill thespace bee When the armature 36 of .theoff-normalassembly is cammed away from engagement with sleeve 41 and the armature53 and the surface tension of the mercury within the armature exerts adownward pull upon the armature to normally hold the contact portion 55firmly against the contact 5| of the back contact member 43."

The mercury within the armature also engages the lower end'of thecontact member 54 whereby mercury is conducted along such member to itsupper contact portion 155 and in the normal position of the armaturetothe contact portion 5| thereby establishing a mercury contact betweenthe contact members 55 and 5!. i a a the pole-pieces 32 and 33 all ofthe flux generated by the permanent magnet 34 is permitted to throughthe armature 53 ofthe switchelement and the armature rises within theguide sleeve 41:

to center itself within the magnetic field thus created, but will berestrained in its movement i the contact portion 55 of the contactmember 54 quickly out of engagement with the contact portion 5| of theback contact member 49 and into engagementwith the contactportion 52 ofthe front contact member 50." Mercury adhering to the contactmember 55is now transferred to the front contact member mercury therewith.

Since the armature 36 is cammed away from the pole-pieces 32 and 33 onlymomentarily, it is quickly restored to establish a low reluctance shuntof the armature 53 of the switche'lement whereupon the magnetic pull onthearmature 53 is reduced permitting the surface tension of themercurypool to pull" the armature 53 back into its normal or retractedposition but sincethecontact areas of the contact portions 52'and 55 areboth relatively large, the film of mercury between them will persistunbroken due to the mercury being drawn into thefilm up the ducts ofmember 54 while the armature 53 moves in its retractive' movement underthe influence of its weight and the surface tension of the mercury pool,until the film'finally breakswhereupon the contact portion 55 snapsquickly into engagement with 1 the contact portion 5| of the backcontact member49.- This switch elementtherefore effects a quick make anda slow break of its front contact closure which break should be in theorder of 30 i or .40 milliseconds and a quick break and a slow i make ofits back contact closure. The off-normal switch assembly is effective totransfer the substation line from the telephone set to the harmonicgenerator andsuppression coils of the call i transmitter as will belater described.

tween such surfaces. The surface tension, of the 7 5 Thesuppression'switch assemblies IBA, I03

and IE0 are similar in construction to the offnormal switch assembly 9just described except,

for the construction of the camming' ends of their associated operatinglevers 22, 23, 24, 25, 26; and 21. The armature 51 of the switchassembly IBC is pivotally supported on the same pivot screw I3 uponwhich thearmature 35 of the off-normal switch assembly 9 is pivoted; thetwo armatures switch 52 to establish a film of being: suitably spacedapart by the spacer 58 supported on the pivot screw I3. andinterposedbetween the armatures. The suppression switch assemblies IDA and MB havetheir armatures 59' and 60 pivotally supported on the pivot screw Hwhich. extends through the ear I6, through aligned holes in the flangesof the armatures and into a threaded hole in the side plate BI- which.supports one end of the key-set.

7 Each of the suppress-ion switch assemblies is so arranged. that itsswitch element may be operated either in response to the depression of akey-set key, in response to the'releasing movement of an operated key orin response to both movements of the key, dependent upon the impulsecode employed. For controlling the operation of these switch assembliestwo operating levers are associated with .each assembly, levers 26 and21 connected to U-bars B5 and, B6, respectively, being associated withassembly IIlA, levers 24' and 25 connected to U-bars B3 and B43respectively, beingassociated with-assembly MB, and levers 22 and 23%connected to U-bars BI and B2, respectively, being associated withassembly II'IC.

Referring now to Figs. 4 to 6, inclusive, the lever 23 has a cam member62 pivotedat 63 to the end thereof, the tail portion 64 of such memberbeing normally held by the leaf spring 65 against the stop pin 66, alsosecured to the lever 23. The leaf spring 65 is provided with twoparallelly disposed ears 6'! bent atright angles thereto and positionedon; either. side of the upper edge of the lever 23 by which the springis riveted to the lever. I

The outer end of the camming portion 62 normally extends through theopening 6-8 in the armature 5'1 of the assembly I-OC above the uppercamming surface of the cam portion 69 of the armature. When the cammember 62 is moved downwardly by the lever 23 upon the depression of akey of the key-set, such member engages the upper edge of the camportion 69 and the member therefore tends to rotate in acounter-clockwise direction. Since, however, the cam member 62. isprevented from rotating in a counter-clockwise direction by the stop pin56, the member is effective in its downward movement to cam over the camportion 69 and thereby move the-armature 51 from its bridging engagementwith the pole-pieces I and II of the switch assembly IUC. The armatureof the switch element of such assembly is thereupon quickly moved to aposition in which its movable contact is disengaged from its backcontact and is engaged with its front contact. As the member 62continues its downward movement it moves pastthe cam portion 69 of g thearmature 51 into theopening 12 thereby permitting the springylfi toreengage the armature 51 with the pole-pieces) and II whereupon thearmature of. the associated switch element is restored to normal to moveits movable contact out of engagement with its front contact and intoengagement with its back contact.

When the depressed key is released and lever 23. is permitted tov rise,the end of cam member 62- carried thereby engaging the lower edge of thecam portion 69 of the armature the cam member 62 I rotates in aclockwise direction against the aeeaevr closed Fig. 6 Normally, thiscammember 13* extends throughtheopening 68 in thearmatension of leafspring 65. without causing the I armature to be cammed out of its normalposition. Therefore, the associated switch element is not operateduponthe releasing or upward movement with the same switch, assembly WC hasits cammember [3 reverselypivoted to the lever as disture- 51 and whenthe lever 22 is depressed'in response to the depression of akey-set key,the member I3 is moved downwardly into engage ment with the uppersurface of the cam portion 69 of the armature, and such member rotatesin. a counter-clockwise direction against the tension of the associatedleaf spring 14 without cammin-g the armature away from the ends of thepolepieces I0 and I I, until it snaps off of'the cam per-i tion 69 andremains positioned in the opening T2 of the armature'when theoperatedkey is fully depressed. 7

When the depressed key is released and lever 22is permitted to rise; thecam portion 1s engages the lower surface of the cam portion 69andtherefore tends to rotate in a clockwise direction;

' apparent that the depression of lever 23 is effective to cause thefunctioning of the switch element of the assembly- I'DC only during thedepression movement of the lever 23and that the depression of lever 22iseffective to cause the functioning of the-switch element of theassembly ,IilC only during the return movement of lever" 22. The switchassemblies IOA and IOB are oper able in a similar manner by theirassociated levers.

'The U -bars BI, B3 and B5 through their associated levers 22, 24 and26'may be considered as rip-stroke barsrand the U-bars, B2, B4 and B6through their associated levers 23, 25 and 21' may be considereddown-stroke bars.

To illustrate the manner in which the call 9 transmitter functions itwill be assumed that the key member KI for transmitting, impulses of acode for the digit 1 is depressed. By reference to the following tableit will be noted that for" the digit 1 it is necessary to operatetheswitch assembly IUA to suppress frequency a during the down-stroke ofthe key KI nd to again operate the switch assembly IDA to suppress thefr equency a during the up-stroke of key KI whereby.

two suippressions of frequency a are effective at the central ofiicesender. To accomplish this, the; under-surface of the key member Kl isprovided with an extension I6 which engages the l pp r edges of bothU-bars B6 and B5 so that; upon the down-stroke of the key member both ofthese" U-bars are depressed. The depression of the. U-bar B6 throughthe-associated lever 21 causes a timed operation of the switch elementof the switch assembly IDA andthrough the off-normal bar 31' andassociated lever 36. causes a timed] operation of the switch element 35of the off-I normal switch assembly 9 whereby the frequency a. ismomentarily suppressed.

The depression of the U-bar B5 is not effective,

through its associated lever 26 to operate the switch assembly [0Aduring the down-stroke movement of such U-bar and lever but when thedepressed key is released and the depressed U-bars B6 and B5 arereturned to normal by their associated springs 29, the lever 26 iseffective to,

again operate the switch element of theswitch assembly IOAand at thesame time the up-stroke of the operated off-normal bar BI- under theinfluence of the retractile spring 29 causes the operation of the switchelement 35 of the offnormal switch assembly9 whereby the frequency a isagain suppressed for ashortinterval.

The keys KI to KIO; inclusive, of the key-set are so designed thattheyare efiective to operate the U-barsBI to B6,inclusive, and thesuppression switch assemblies IOA, I03 and I to control thesuppressionof frequencies a, b and c finder LF to hunt for and establisha connectionwith the calling line, after which the line finder-firstselector link becomes associated over the sender link SL with an idlesender. Upon the association of the sender with the substation a circuitis established from battery over brushes of the trunk finder TE andsender selector SS, conductor 900 and windings of relay I000 I toground. Relay I000 operates and closes an 0bin themanner indicated inthefollowing table: vious operating circuit for relay I002. Relay I002 KeyK1 K2 K3 K4 K5 K6 K7 K8 K9 K10 U-bars operated. B9, B5 B2, B1 B4, B3 B2,B3 B6, B1 B2, B5 B4, B5 B2, B1, B3 B4, B1 B2,,Bl, B5 Switch operated on,down: 3 I I stroke 10A 10C 10B 10C 10A 10C 10B 10C 10B 10C Switchoperated on 'up- I I I I stroke 10A 100 I 10B 10B 10C 10A 10A 10C Thecall transmitterIof Figs. 11 to. 8, inclusive,

is applicable to a wide variety of types of idial switching systemsandtparticularly to those of the I type in which register mechanisms areemployed at the central office for. registering the designationstransmitted for controlling the sclective operation of automaticswitchesto complete connections. Accordingly, the system upon operating connectsground over its right contacts to off-normal ground conductor I003, toprovide locking ground for other relays of the sender and over its leftcontacts and conductor circuit is established therefrom over the leftback chosen to illustrate the invention is one injxwhich l the centralofiice is equipped I with! automatic switchesof the panel type and withregister send! ers for registeringthe designations transmitted to thecentral ofiice from subscriber stations. It

will be obviousIthat other forms of switches may be used forestablishing connections such as I switches I of the well-knownstep-by-step and crossbar types. I I. 1 l I Referring to Figs. 9, 10 and11 of the draw ings, a subscribers line is shown appearing inthe contactbank of the linefinder LF. The line are necessary for an understandingof the present invention. The number of registersemployed in thesesenders will, of course, vary with the requirements of the'exchangearea. In some of the" larger areas ofl'lce codesrequire two or threeoffice code digit registrations and the numerical part of thedesignations usually requires four registrations. In the presentdisclosure three office code digit registers A, B and C are shown inFig.l1 and the' units numerical register U is also shownfitbeing understoodthat the thousands, hundreds and tens numerical registers would be,provided and inserted between theunitsregister U and the ofiice codedigit register C. These registers each comprise five register relayswhich are selectively operated under the control of the siX recordingrelays AD BD, CD, AU, BU and CU and thefrequen'cy receiving channels Fa,Fb, Fc of Fig. 10. I I

It will be assumed that to initiate a call at the substation illustratedin Fig. 9 the subscriber removes the handset H of the substationinstrument from the cradle Iwhereupon a'circuit is established over, thesubstation line to the central 'ofiice which is instrumental in causingthe line-,

contact of relay I009, conductor IOI0 to battery through the winding ofprogress relay H06, whereupon relay I I06 operates and locks in acircuit from battery through its winding and the winding of progressrelay II01, over the outer left front contacts of relay I I06, and overthe back contact of progress relay II I I to ground on conductor I003.Relay IIOI does notoperate in this locking circuit sinc itswinding isshunted as long as ground remains connected to conductor I M 0. Whenrelay [I00 operatesa circuitisalso establishedfromground on conductorI003 over theback contact ofI relay III I, the outer left contacts ofrelay H06, conductor IOII and to battery through the rightnormalcontacts and Winding of relay I009. operates, locks overfits rightalternate contacts to ground on conductor I003 and at its back contactremoves ground from conductor I M 0,

whereupon relay II 0-! I operates in the locking circuitofrelay H06;prepares operating circuits for relays H00, IIOI, II02, II04'and H05 ofthe first code digit register A over conductors I030, I03I, I032, I034and I035; and at itsright contactsconnects ground to conductor IO0I toshunt the rightwinding of relay I000 whereby the cur- I rent flowing,over the operating circuit of relay IO0Iis increased as a signal to theline finderselector link. I I

, Relay 90I, upon operating, connects the winding of battery feed relay902 to the calling line substation over a circuit which may be tracedfrombattery through the left winding of relay sender selector SS, brush904 of the trunk finder TF, contact of sequenceswitch cam 905, brush 906of line finder LF,thering conductor of the calling line, switchhookcontacts 901, the back contact of the oir-normal switch assembly 9,

through the transmitter 908, the left winding of ring contacts'ofrelayI; the right winding of I relay 902and the normal contacts of relay BMto ground through the secondarywinding of the dial tone coil 9I5.I Relay902 operates over this Relay I009 thereupon 902, the left contacts ofrelay 90I, brush 903 of,

circuit and, dialing tone is applied thereover to apprise the callingsubscriber that he may proceed to key upthe digits of the desiredtelephone number. Relay 902, upon operating, establishes anobvious'circuit for relay 9I6 which also operates to prepare anoperating circuit for relay 9 I4 and relay 902 establishes a circuitfrom ground over its left contacts, conductor 9I'I, over the uppernormal contacts and through the winding of relay I005, and throughresistance i001 to battery and, in parallel therewith, through thewinding-of relay I009 and resistance I000 to battery. Relay I005operates and looks over its upper alternate contacts to ground onconductor. 1003, but the winding of relay I096 being shunted so long asgroundis applied to conductor 9.I I, does not operate. The closure ofthe lower front contact I005 is without function at this time.

,In response to the reception of dial tone, the

calling subscriber proceeds to key up the digits of the wanted linenumber which numberjit will be assumed is CHE-1067. j When the key K2,which in addition to the digit value 2 has the letter designations ABC;is depressed to transmit signal impulses for the firstco'de letter C,the off-normal 'sfw'itch assembly 9 is momentarily operated and thenreleased during the down-stroke of the key and in the interval thatthem-ovable contact of such switch assembly is in engagement with thefront contact thereof, the suppression switch assembly WC is momentarilyoperated. Again when thedepressed 'key is released, the off normalswitch 'assembly 9 is momentarily operated and released and'during theinterval that the movable contactof suc-lrassembly 'is'in engagementwith the front contact thereof, the suppression switch assemblyl 0C isagain momentarilyoperated for 'a purpose to be later described.

' l he movement of the movable contact of the off-normal switch assembly9 from its back or normal contact position disconnects the subsettransmitter 908 from its bridged connection across the substation lineand the engagement of the movable con-tact with the front contact,connects the harmonic generator 921 in series with,

the suppression'coils 922 and 923 and'condenser 9I8 across the line.There being'no direct currentbridge across the substation line at thesubsta tion so long ast he movable contact of the off-normal switchassembly!) is out of engagement with its back contact, relay 902 of thesender releases in turn opening the circuit of relay'9I6 and removingground from conductor 9H. Relay '9I6, however, being slowto release doesnot-release during the interval that the movable contact of theoff-normal switch assembly is disengaged from its back contact. Withrelay 902 released and relay 9I-6 operated, an obvious circuit isestablished for relay '9I-4 which operates and at its contactsdisconnects the secondary windingofuthe dial tone coil 9I5 from thecalling line loop to discontinue the application ofjdialtone currentthereover and connects direct ground to thecalling line loop. Theremoval of ground from conductor 9I-1 removes 6 ass ntcircuit tracedfromthe sender to the tip cond lator-Diane calling line,through-condenser 9I8, coils 923 and 922, the two windings ofeach ofwhich coils are wound to be series opposing, through the coil oftheharmonic generator 92I, over. thefront. contact of the off-normal switchassembly 9, over the switchhook contacts 901 over the ring conductor of,the calling line and thence over the circuit previously traced tothethereupon travel back to the central oflice where they passthrough thebase'frequ'ency elimination filter 9I9, shielded transformer920, throughcircuit X and thence through the primary windings of the inputtransformers associated with the receiving channels Fa, Fb, Fc and V. 7

Associated with each input transformer such as l0l 3, is'a frequencyreceiving" channel'con-l sisting of a secondary winding of suchtransformer,=a seriestuned circuit IOI4, a single vac- .uumtu-be such asI0 I 5 with a feedback through the copper-oxide units, such as IIII6,and a relay, such as I0'I'I. Initially the vacuum tube is biased nearlyto cut-off. A small received signal is amplified and fed back throughthe condenser :IOI8 and the copper-oxide units -I0I6 to charge up thecondenser I019. This condenser is poled to reduce the negative bias onthe grid of the tube I015 with the result that the gain of the tube isincreased and the amount of voltage on the grid is increased further.The final result is that a .relativeiy'smallzsignal su'ilicie'nt to.produce a sharp rise in plate current through the winding of relay MIT.The sensitivity of each individual channel is adjusted by means of thevariable resistance, such as I020. This method of controlling thesensitivity by changing the alternating current feedback-does not affectthe tuning-of the channel. From the foregoing. it

will be apparent that each relay such as IOI'I of each channel willrespond to a single frequency with a relatively high discriminationagainst the others.

In the present description, it will be assumed that the first :channelFa is tuned to the a frea quency harmonic generated bythe coil 921 of700 cycles; the second channel Fb is tuned to the b frequency harmonicof 1:100 cycles and the third channel F0 is tuned tothe 0 frequencyharmonic of 1500 cycles. .Since all harmonics of the base frequency aretransmitted back over the line by the generator 924 before any one-ofthe suppression-switches has had time to function, the channels' allinitially respond and their associated channel relays -I'0I-I I023 andI024 are all operated. With these channel relays all operated, a

a series circuit is established over their front consion coil 923overithe front contact of the switch :IDC andtover the front contact ofswitch 9 and thes'wit'chhook contacts 901 'to the ring side of the linewhereby the condenser Cc is elfective to suppress the frequency o I of1500 cycles, whereuponIrelay lfll'hofthereceiving channel E'creleases,relays I023 and I024, however, remain:

ingoperated. Relay IOI'I, upon releasing, opens I which releases, afteran interval. I I I ;Relay LOH upon releasing and before relay over thecontacts of relay I026, the back contact of relay IOI'I, the middleright back contact of transfer relay I02 I, through the winding of re-,cording relay CD to battery. RelayQD, thereat its front contactthecircuit of relay I026 I026 releases, establishes aIcircuitIfromground upon operates, looks over its inner left contacts i to groundover the back contact of release relay I022, and at its outer leftcontacts prepares a circuit forrelay I02I. Upontheterminationof thesignaling period, when the off-normal switch assembly 9 reestablishesthe direct currentbridge atthe substation through the subset-transmitter, relay 902 reoperates-t o establish t e circuit offrelayllfli and toreconnect groundtto con-J ductor 9|! whereupon such ground is extendedover the upper front eontact of relay I006 to a c is; suppressedresulting in the releaseof channel relay I0" and the release of relayI026.

During the releasingtime of relay I026 and with transfer relay I 02Ioperated, a-circuit is established from ground over the contacts ofrelay I026, the back contact of relay IOI'I, the middle right frontcontact of relay I02I to battery through the winding of recording relayCU. I Relay CU, upon operating, looks over its left contacts to groundover the, back contact of relay When the offenormal switch assembly 9again releases, relay 902 ,reoperates and causes the reoperation ofrelay I005, over the circuit previously traced. With relay I005Hoperatedand relay I006 unoperated, a circuit is established from ground: overthe lower front contact of relay I005, the lower back contact oflrelayI006, the

right back contact of relay AD, the No. 2 right back contact of relayBD, the No. 2 right front contact of operated relay CD, the No. 2 rightback contact of relay AU, the No. 3 right back 1 contact of relay BU,the No. 5 right front conpoint between the Winding of relay I005 and re-I sistance I001. Relay I005 being now shunted releases IRelayI I006 is,however, maintained operated-following the release of relay I005 over acircuit from ground on conductor;0l1, over the upper normal contacts ofrelay I005, through the winding of relay'I006 and resistance I008tobatterylff With relay I005 released and relay I006 operated,the-circuit of relay I02I is now completed fromground over the lowerbackIcontact of relay I005, the innerlower front contact of relay I006,the outer leftIcontacts of relay CD to battery through. the winding ofrelay I02I; Relay I02! now operates,,locks over its inner right frontcontact to ground over the right back contact of relay I022; at its backcontacts disconnects the windings of recording relays nd CD from thecontacts of the channel relays] I023, 1024' and I0II,Y respectively;rconnects the windings of recording relays AU, BU

and CH with the contacts of the channel relays allofI which are atthistime operated andat its outer right front contact prepares a circuitfor relay I022. When the off-normal switbhassem- I bly 9 restores toitsnormal position thus discon necting the harmonic generator fromthesubstation line, the frequencies .a, band 0 are no longer generatedand. transmitted to the receiv ing jcl iannels of the sender and channelrelays I023, I024 and ljflll thereupon'fall; release, but

relay I026 being now released, the channel relays are ineffective I toestablish circuits for e the recording relays s I s i I During thereturorjup-stroke movement of the operated key K2, the off-normal spring assembly 9 is again operated and released and during that interval, thesuppression switch assembly IBC is againIoperated and released to "againsuppress the frequency 0. During, the in terval that theIdirect currentloop at the sub- I relaysfalloperated, relay I026 again operates. inresponsefto the momentary operation of the tact of operated relay CU,conductor I032,the No.v 3, left contacts of progress relay IIO'I tobattery through the right winding ,of relay H02 of the A code,digitregister Relay II02 thereupon operates and looks over its leftwinding and left contacts to-ground onwconductoz-I I003 and withtheremaim'ng relays LIIOI, pI I04, [I05 and I I00,

of the A register unoperatedserves to register thefirst office codeletterC. {The removal of the I harmonic generator from the calling linewhen the off-normal switch assembly is fully restored causes thereleaseof all, of the ,channel relays I023,I024and|0l1.

A c'ircuitis also establishedhupon the operation of relay I005 fromground over its lower, front contact, the lower back contact of relayI006, over the outer right front contact of relay II02I to batterythrough the winding ofrelay I022 which operates after anIintervalsufficient to insurethat the digit signals recorded by the operation ofrecording relays have been effective to cause the registration thereofin a digit register of the sender; atits Ibackcontact opens the lockingcircuit of the-operated recording relays, in the case assumed relays CDand CU which thereupon release; opens the locking circuit of transferrelay I02II which-releases; and at its front contact establishes Ianobvious circuit for relayl025. Relayl025 operates, locks over its frontcontact to off-normal ground on conductor I003, and at its left contactsprepares a circuit for ,operatingthe progress relay III6. When relayI02I releases, relay) I022 also releases,

When: the subscriber depresses the key K4 for the second oilice codeletter-H which has a numerical value; of (l; the off-normal switch assembly9 is operated momentarily to open the direct current loop atthesubstation and to connect the harmonic generator 92L to thesubstation line. Duringthe ,interval that the switch is thus operated,the frequency suppression switch I00 is momentarilyoperated. With thegenerator connected to the line, all of the chan-I nel relays I023, IBMand Hill operate, followed by the operation of relay I026 and when theswitch is momentarily operated to sup press frequencyc ,channel relayIOI I releases in turn causing the release of relay I020. Dur

ing the releasingtimeof relay I026 and with suppression iswitcliassembly IOC, the frequency 715 transfer relay I02! now released, acircuit is established from ground over the contacts of re1ay I 026, theback contact of relay IOII, the

operated and relay I025 operated, a circuit :is'

established 'from ground over the lower :front contact of I relay 1-005, the lower ffront contact of cassava 'tery through the winding orrecording rilay'iBU.

Relay upon-operating looks over its left com tacts under thec'ontrol ofrelay 'I 02-2.

When the oiT -normal switch assembly is again restored, the harmonicgenerator 021 is disconnected from the substation line resultin in therelease -of all or the channel relays W023, I020 and 00H and th directcurrent loop is reestablished at the substation, resulting inthereoperaitlon of relay -902, followed by the reopera tion of :relay "I005as previously described. With relay I005 operated, and relay -I'0'06unoperat'ed,

relay I006, the left contacts of relay I1I25,-c'onductor I012, the.right front contact of progress relay '1 I00 to battery through the{winding of progress relay I II B. 'Rel'a'y' Il lfi operates andlocksthrough its winding and the 'wm'ding of progress relay @I I'l overthe left contacts of relay fIIIiIB and the back' contact of progressrelay N27 to groundon conductor 1003. Relay 1:110 being shunted-soaring:as ground remains "connected to conductor -12 does not operate.

1 When the on-normal switch assembl 0 is restored, the transmission ofharmonic "frequenciesby generator '92I :eeasesLandall of the operatedchannel relays 1023, M024 and lfl-l 'l release and the directcurrent-loop is reestablished at the 'substation resulting in thereoperat'ion "of relay -902 and the reconnection ofgroun-d to conductor9II. As before described, relay I006 -is now held operated tothis ground'and-rel-ay 4005 is shunted and releases. With-relay l005 release'd andrelay I006 operated, the *c-i'rcuit of -tr-ansfe'r relay I02 Ipreviously prepared through the operation of recording relay CD iscompletedand relay'I02I operates and locks as previously-described underthe control er relay 1022. Relay I005, upon releasing, alsoremovesgroundirom conductor I-0I'2 whereupon progress relay II I1operates in the "locking circuit of relay III B;

connects the windings of the relays or "the code digit register to Lconductors I 031, I 032, 1030, I035 and 103-0, extending to cont-acts ofthe *recording relays, and 'at its back contact opens the lockingcircuit of relays I I 0 0-and I' I G'I which now release since theiroperating "circuit was opened upon the 'prev-ious-"operationof relayI000.

Uponthe up- 'strolce of the depressed --key "K4, the off-normal switchassembly 9 is again momentarilyoperated to open the direct-current loopat I the substation and to connect the harmonic generator 92I to thesuhstatic'm line; With the a circuit is established from groundover"'-the lower none contact-of relay 0005, the lower back contact-orrelay N106, the right back contact of relay AD, the No. 2 back contactof reIayBD,

the N0. 2 right front "contact of relay CD, the No. 2'=rightback contactof relay AU, the "No.3 right from; contact -of relay BU, the No. 4 rightback-contact -of -'relay-'CU,--conductor I030, over the No. 4 1e'ftcontacts of relay IN 1 through the winding or relay --I I I! of theoflice code register B to battery. Relay "I H 4, upon-'oper'ating locksover its left winding and left contacts to ground =on conductor I003 andwith the ;remaining relays of the B register *unoperated, serves toregister the second "ofiice code -letterH. The operation of relay I005with relay' "I000 unoperated, also establishesthe previously tracedcircuit of relay 102-2 which operates after'aninterval to cause therelease of the operated re"- cor'din'g relays CD :and EU and the releaseof the transfer relay I02I. leases,-'relay' I022 alsoreleases. I

*Wheh'the subscriber'depresses the key K3 "for thethird ofiice codedigit 3, the. off-normal switch assembly is operated 'momentarily 'toopen "the direct "current 'loop at the substation and connects theharmonic generator 9'2I to the sub: station line. During theinterval'thatjtheswitch is thus operated, the-frequencsuppression'switch I 03 is -momentarily operated. With the "generatorconnected to the-line, all of the channel "regenerator reconnectedtothe'line, the -receiving 7 channels 'of the sender all respond"toth'egenthe back contact 'of switch 10A to the ring "side of the lineto suppress th frequency-b whereupon the channel relay I024releases'followedhy the release of relay I020. With'transfer relay I02Inow operated, a circ'uitisestablished 'during the releasing time ofre1ayI020 from "ground over its contacts, the'bac'k contact ofrelayiOZI,

the inner leftiront "contact of ma -"I 021'hatlays 1023, 1-024 and-IOI'-'I operate'followed 'bythe operationo'f relay I026 andwhen theswitch 103 is momentarily operatedto suppress the'frequency b, channelrelay 'I024're1ea'ses'in turn causingrthe release of "relay "I026.During "the releasing time-of relay I026 and with transfer relay -I02Inow released, a circuit is-establi'shed from ground over the contacts of'relay I 0 26, the back contact of relay I024, thednnerleftbabk contactof relay I02I to battery through the winding'o'f therecordihg rela *BD.Relay"BD,.upon operating, locks under'the'control ofrelay' I022 andprepares a circuit for relayfl'02l as previously described. 'When theline loopls opened atthe substation by the oifenorma'li'switch assembly9, relay 002 releases and by removing ing of progress relay "l -I20.Relay I I26 operates and locks through its winding and'the winding ofprogress relay -'I-I2I"-'ovei"the left contacts ofree' lay I 'and'toground'on conductor I003, over the back contact of the progress'relay"(not. shown) associated with'th thousands "digitreg- I isterandcorresponding "to "progress "relay "H21;

When 'relay 'I 02'I re- Relay II 21 being shunted does not operate solong as ground remains connected to conductor IIII2. I I I Whentheoif-normal switch assembly 9 isrestored, the transmission of harmonicfrequencies by the generator 92I ceases andall of the operated channelrelays I023, I024 and I" release and the direct current loop isreestablished at lay 902 and the reconnection of ground to conductor 9 II. As before described, relay I006 is now held operated tothis groundand relay I005 is shunted and releases.

' and at its right back contact opens the locking circuit of progressrelays III6 and III! which.

now release since their operating circuitlwas opened upon the removal ofground from conductor IOI2. r

Upon the up-stroke of the depressed key K3, the ofi-normal switchassembly 9 is again mo- ,mentarily operated to open the direct currentloop at the substation and to connectthe har .902 releases removingground from ground conductor 9I'I whereupon relay I006 releases aspreviously described. During the interval that the ofi-normal switchiSthllS operated, the frequency suppression switch assembly IOB ismomentarily operated to suppress the frequency b'whereupon the channelrelay I024. releases, followed by the the substation resulting in thereoperation of rerelease of relay I026. With transferrelay I 02I nowoperated, a circuit is established during the releasing time of relayI026 as previously described through the winding of recording relay BU.Relay BU, upon operating, locks overits left contacts under thecontrolof relay I022.

When the off-normal switch assembly 9 is again restored, the harmonicgenerator 92I disconnected from the substation line resulting in therelease of all of the channel relaysl023, I024 and I0" and the directcurrent loop is established at the substationresulting in, the reoperation of relay 902 followed by the reoperation of relay I005 aspreviously described. With relay I005 operated and relay I006 unoperateda cir-- cuit is established from ground over the lower front contact ofrelay I005, the lower back contact'of relay I006, the rightback contactof relay. AD, the No. 3 right front contact of relay BD, the No. 3 rightback contact of relay CD, theNo. 3 right back contact of relay AU, theNo, 5right front contact of relay BU, the No. 6 right back lishedfromground applied over the right back tactof relay BD, the No. 4 right backcontact of relay CD, the No. 7- right from contact of relay BU, the No.5 right back contactof relay CU, conductor I032, theNo. 3 left contactsof I progress relay N21 to battery through the right winding of relay II22 oftheC code digit register. Relays II2I and H22, upon operating,lock over their left windings and left contacts to ground on conductorI003 andwith the other relays of the C code digit registerunoperated,serve to registe the third office code digit 3. I I The operation ofrelay I005 with relay I006 unoperated, also establishe the previouslytraced circuit of relay I022 which operates after an interval tocausethe release of the operated record- I ing relays BD and BU and therelease of transfer relay 102i I followed by the release of relay I022.

In asimilar manner in response to thekeying of the thousands numericaldigit 1, the frequency a is suppressed once in response'to the operationof the switch assembly IOA upon the depression of the key KI and againupon the release of such key, resultingin the operation of recordingrelays AD and AU. In response to the keying of the hundreds digit 0,the1frequency e is suppressed upon the depressionof. the key Kl0 through thekeying-of the tens digit 6, the frequency 0 is suppressed upon thedepression of the keys K6 through the operation of the switch assemblyIIIC and thefrequency a is suppressed upon the release of the depressedkey upon the operation of the switch assembly IOA resultingin the opera:tion of the recording relays CD and AU and in responseto the keying ofthe units digit 7, the frequency b is suppressed upon the suppression ofthe key Kl through the operation of the switch assembly [03 and thefrequency ais suppressed uponthe release of the depressed key through.the: operation ofjthe switch assembly IOA. operates it connects themid-point between; the windings of coil 922through condenser Co to thering side 3 of the line and renders switch 103 ineffective. I I

With recording relays AD and AU operated in response to the keying ofthe thousands digit 1, I

Contact of relay on, the No. 1 right front contact of relay AU, the No.2 right back contact of relay I BU, the No. 6 right back contact ofrelay BU to conductor I03I andthence over the No 2 left contacts of anoperated progress relay; similar .tO-relay I|0I but associated withthethousands digit register, to battery through the winding of a 'relay ofthat register, corresponding torelay,

IIOI, whereby such relay operates and locks-and with the other relays ofsuch register unoperated, I registers the thousands digit I 1. 4 I

With recording relays CD, AU and CU operated, in responseto the keyingof the hundreds digit 0, then when ground is applied to the rightarmature of relay AD, a circuit is estabsished over the right backcontact of relay AD, the bio. 2 right back contact of relay BD, the No.5 right contact of relay AD, the No. 4 right front con- I It is to benoted 'thati'when switch I0A front contact of relay 'CD, the No. 5 rightfront contact of relay AU, the No. 4 right back contact of relay BU, theNo. 3 right front contact of relayCUto conductor I030 and thence overthe No. 1 left'contacts of an cperated'progress relay, similar to relay.IIfl'I but associated with .the hundreds. digit register, tobatterythrough a winde ing of arelayof that register corresponding torelay I I00, whereupon such relay operates and locks to register thehundreds digit 0.

With recording relaysCD and AU operated, in response to the keying ofthe tens digit 6, then when ground is applied to the right armature ofrelay, AD, a'first circuit iscompleted over the right back contact ofrelay AD, the No.2 right back contact of relay BD, the No. 2 right frontcontactof relay CD,,the No. 2 right front contact of relay IAU, the No,2 right back contact of relay the No. 6 right back contact of relayCUfcoriductor I03I and thence over the No. 2 left contacts of anoperated progress relay, similar' tojre'la'y H01 but associated with thetens I digit register to battery through the winding of aremy of'su'chregistercorresponding to relay Ill! I, whereupon such'relay operatesandlocks. A j'circuitis also established from ground applied oVjertheright back contactof relay AD, the No. 2 right back co n'tact of relayBD, the No. 5 right front contact ofrela CD, the No. 5Qright frontcontact ofrelay AU, the No; 4 right back contact of'relay BU,'the' No. 1right back Contact of relay CU, conductor I035 and thence over the No; 5left contacts'of an operated progress relay, similar to relay I I! butassociated with thetens frontcontactofsrelay 'BD, the No. 4 right backcontact of relay CD,.the N o. 4 right front contact of'relayAU, the No.6right back contact of relay BU, theNo. right back contact of relay CU,overconductorlflfl and thence over the No. 3 left contacts of, theoperated progress relay IIG'I to battery through the right winding ofrelay I I62 of the units digit register U. A second cir- 'cuit is alsocompleted over the right back contact of relay AD, theNo. 3 right frontcontact of relay BD, the No. 3 right back contact of relay CD, the No. 3right front contactof-relay AU, the No. 4 right back contact of relayBU, the No. 1 right back contact of relay CU, over conductor I035 andthence over the No. 5 left contacts of relay II 6''! to battery throughthe right winding of relay H65 of the units digit register U. Relays H62and H65, upon operating, lock over their left windings and leftcontactsto ground on conductor I I I303 and with the other relays ofthis register unoperated, serve to register the units digit '7.

'QAllof the digits of the wanted line number keyed by the subscriber arenow registered in the sender and the sender may proceed to controlselector switches to extend a connection over the district selector Sand other selectors (not shown) in accordance therewith after which thesender link SLis released to release the sender to make it available forother calls.

In the preceding discussion, the keying and registration of letters ordigits having the digit values'l', 2, 3,4, 6', *7 and0 have beendiscussed;

If the digit 5 is keyed by the operation of key K5,

then upon the depression of the key, switch assembly WA is operated tosuppress the frequency a and upon the release of theldepressed key, thei switch assembly IIlC is 'operatedlto suppress the frequency 0resulting in the operation of the recordingrrelays AD and CU. With theserelays operated, then when ground is app-lied to the right armature ofrelay AD,-a circuit is completed over the right frontcontact of relayAD, the No. 1

right back contact of relay BD, the No. 1 right back contact of relayCD, the No..1 right back contact of relay AU, the No. 1 right backcontact of relay BU, the No. 1 right front contact of relay CU toconductor I035 to cause the operation of the relay of a register, suchas relay I I05 of the first code digit register A.

If the digit 8 is keyed by the operation of key K8, then upon thedepression of the key, the switch assembly IOC is operated to'suppressthe frequency 0 and upon the release of the depressed key, the switchassemblies IOB and I0C are operated to suppress the frequencies b and 0'resulting in the operation of recording relays CD,

BU andCU. With these relays operated, then 7 when ground is applied tothe right armature of relay AD, a first circuit is completed over theright back contactof relay AD, the No. 2 right back contact of relay BD,the No. 2 right front contact of relay CD, the No. 2 right back contactof relay AU, the No. 3 right front contact of relay BU, the No. '6 rightfront contact for relay CU, to conductor I'03'I. A second circuit iscorn pleted over the right back contact of relay AD, the No. 2 rightback contact of relay BD, the No. 5 right front contact of relay CD, theNo. ,5- right back contact of relay 'AU, the No. 6 right front contactof relay BU and the No. 5 right front con-v tact of relay CU toconductor I032 and a third circuit isestablished over the rightfrontcontact of relay AD, the No. 2 right back contact of relay BD, the No. 2right 'front contact of relay CD, the No. 2 right back contact of relayAU, the No. 3 right front contact of relay BU and the No. 2 right frontcontactof relay CU to conductor I035, With ground applied to conductorsI03I, I032 and I035, relays of a digit register, such as relays I IOI,H02 and I I05 of the first code oligitregister A, are operated toregister the digit8.

If the digit 9 ispkeyedby the operation of key K9, then upon thedepression of the key, the switch assembly 'IIlB is operated to suppressthe frequency'b and upon the release of the depressed the armature ofrelay AD, 2. first circuit is com-1 pleted over the right back contactof relay AD, the No. 3 right front contact of relay BD, the "No. 3 rightback contact ofrelay CD, the No. 3 right back contact of relay AU,the'No. '5 right back contact of relay BD, the 'No. '4 right backcontact of relay CD, the N014 right back contact of relay AU, the No. 7right back contact of relay BU and the No. 7f right front contact orrelay CU to conductor I035. With ground applied to conductors I034 andI035, relays of a digit register,

such as relays I I04 and I I05 of the first code" ascaevr digit registerA, are operated to register the digit 9. i

quency in saidline, means at the central oflice selectively responsiveto the harmonics generated at said station, a plurality of keys at saidstation each havinga downand an up-stroke and means controlled by saidkeys for selectively suppressing one of said generated harmonics duringthe down-stroke of a key and for selectively suppressing one or more ofsaid generated harmonics during the up-stroke of the operated key.

2. The combination in asignaling system of a line having a stationthereon, a source of alternating current ofa base frequency at thecentral ofiice, means for connecting said source to said line to supplycurrent thereto; a harmonic generator at said station responsive tocurrent from said source togenerate harmonics of the base frequency insaid line, means atthe central ofiice selectively responsive to theharmonics generated at said station, a pluralityof keys at said stationeach having a downand an up-stroke and means controlled by said keys forselectively suppressing one of said generated harmonics during thedown-strokeof a key and for selectively supsaid generated harmonicsduring the down-stroke of akeyfi an'd for including variable amounts ofsaid reactance in circuitwith said generator for selectively suppressingone ormore of said geno'perated'fkeyp l l -'-5 The'combination:in a.signaling system of a erated harmonics during the up-stroke of the linehaving a station thereon, a source of alternating currentof a basefrequency at the central ofiica means forconnecting said source to isaid line to "supply current thereto, a harmonic generator' atsaidstation responsive tocurrent from said source to generate harmonics ofthe base frequency in said line, means at the central oifice selectivelyresponsive to the harmonics generated at said station, a tuning circuitat said station including a. variable reactance associated with saidgenerator, a plurality of keys at said station havinga down and anup-strokeand a: pluralityof switch elements controlled by said keys-forincludingvariable amounts of said re -3 actance in circuit"with' said 1generator for selectively suppressing one of said generated harmonicsduring the down-stroke of a key and for includingvariable amounts ofsaid reactance in circuit withsaid generator for selectively suppressingone ormore ofsaid generated harmonics duringthe up-stroke of theoperated key..

l 6. The combination in a signaling system of a line having astationthereon, a source of alternating currentof a base frequency atthecentral :ofiice, means for connecting said source to said pressing oneor two of said generated harmonics during the upv-stroke of the operatedkey.

3. The combination in a signaling system of a line having a stationthereon, a source of alternating current of a base frequency at thecentral oifice, means forconnecting said source to said down-stroke ofany operated key and again during the up-stroke of such operated key,means controlled by said switch for connecting said harmonic generator;to said line for atimed interval and means controlledby said keys forselectively suppressing one of; saidgenerated harmonicsduring theoperation of said switch in response to the down-stroke of an operatedkey and for selectively suppressing one or more of said generatedharmonicsduring the operation of said switch in response to theup-stroke of an operated key. l

4. The combination in a signaling system of a line having a stationthereon, a sourceof alternating currentof a base frequency at thecentral ofiice, means, for connecting said source to said line to supplycurrent thereto, a harmonic generator at said station responsive tocurrent from said, source to generate harmonics of the base frequency insaid line, means at the central office selectively responsive to theharmonics generated at said station, a tuning circuit at said station,including a variable reactance associated with said generator, aplurality of keys at said station having a down and an up-stroke andmeans controlled by said keys for including variable amounts ofsaidreactance in circuit with said generator for selectivelysuppressingone of line tofsupply currentthereto, aharmonic generator at saidstation responsive to current from said source to generate harmonics ofthe base frequency insaid line, means atthe central office selectivelyresponsive to the harmonics gen erated at said station, a tuning circuitat said station including a variable reactance associated withsaidgenerator, a pluralityof keys at said station each having a down and anu'p-stroke and a pluralityof switch elements controlled by pressing oneor more of said generated harmonics during the up-stroke of the operatedkey, two of said switch elements being connected in series,

relation "whereby ,if both of them are simultaneously operated by theerroneous operation of two keys the circuitclosureof one of said twoswitches is nullified.

7. The combination in a signaling system of a line having a stationthereon, a source of alternating current of a base frequency at thecentral oflfice, means for connecting said source to said line to supplycurrent thereto, aharmonic generator at said station responsive tocurrent from said source to generate harmonics of the base fre quencyfinsaid line, means at the central oflice selectively responsive to theharmonics generated at said'station', a tuning circuit at said stationincluding a variable 'reactance associated with said generator, aplurality of keys at said station each having a down and an up-strokeand a plurality of timed switch elements controllable by said keys forincluding variable amounts of said reactance in circuit with saidgenerator for selectively suppressing one of said generated harmoniesfor a timedinterval during the downstroke of a key and for includingvariable amounts of said reactance in circuit with said generator forselectively suppressing one or more of said generated harmonics for atimed interval during the lip-stroke of the operated key.

, 8. The combination in a signaling system of a. line having a stationthereon, a source of alternating current of a base frequency at thecentral onice, means for connecting said source to said line to supplycurrent thereto, a harmonic generator at said station responsive tocurrent from said source to generate harmonics of the base frequency insaid line, means at the central office selectively responsive to theharmonics generated and a plurality of timed switch elements controlledby said keys for including variable amounts of. said reactance incircuit with said generator for selectively suppressing, one of saidgenerated harmonics for a timed interval during the down-stroke of a keyand for includingvariable amounts of said reactance in circuit with saidgenerator for selectively suppressing one or more of said generatedharmonics for a timed interval during the up-stroke. of the operatedkey. 9,. The combination in a. signaling system of a line having astation thereon, a source of alternating current of a base frequency atthe central oflice, means for connecting said source to said line tosupply currentthereto, a harmonic generator at said stationresponsive tocurrent from saidsource to generate harmonics of the base frequency insaid line, means at the central ofiice selectivelyresponsive to theharmonics generated at said station, a tuning circuit. at said stationincluding a variable reactance associated with said generator, aplurality of keys at said station each having a down and an up-stroke, aplurality of switch elements for including variable amounts of. saidreactance in circuit with said generator and selectively operable tosuppress different generated harmonics, a pair of bars associated. witheach of said switch elements,

means controlled by the operation of the first bar of any pair foroperating the associated switch element, means controlled by the releaseof the second bar of any pair when operated for operating the associatedswitch element and means controlled by said keys for selectivelyoperating and then releasing said bars to cause the selective operationof said switch elements whereby one of said generated harmonics issuppressed during the down-stroke of a ke and one, or more Of saidharmonics is or are suppressed during the up-stroke of the operated key.

10. The combination in asignaling system of a line having a stationthereon, a source of alternatlng current of a base frequency at thecentral o-flic'e, means for connecting said source to said line tosupply, current thereto, a harmonic. generator at said stationresponsive to current from said source to generate harmonics of the basefrequency in said line, meansat the central office,

selectively responsive to the harmonics generated at said station, atuning circuit at said station including a variable'reactance associatedwith said generator, a plurality of keys at said station each having adown and an up-stroke, a plurality of switch elements for includingvariable amounts of said reactance in'circuit with said generator andselectively operable to suppress difierent gen-'- erated harmonics, apair of bars associated witheach of said switch elements, a cam memberconnectedto the first bar of each pair for momentarily operating theassociated switch element only upon the operation of said bar, a cammem-, ber connected to the second bar of each pair for momentarilyoperating the associated switch ele-- merit only upon the release ofsuch bar and means controlled by said keys for selectively operating andthen releasing said bars to cause the selective operation of said switchelements whereby one of said generated harmonics is suppressedduring thedown-stroke of akey and one or more of said harmonics is or aresuppressedduring the upstroke of the operated key v 11. The combinationin a telephone system of a line having a station thereon, a source ofalternating current of a base frequency at the central ofiice, means forconnecting said source to said line to supply current thereto, aharmonic gen erato-r at said station responsive to current from saidsource to generate harmonics of the base frequency in said line, meansat the central ofiice responsive respectively to the harmonics generatedat the station, a plurality of keys at said station each having a downand an rip-stroke, means controllable by said keys for selectivelysuppressing one of said generated harmonics during thedown-stroke of akey and for selectively suppressing one or more of said generatedharmonies during the up-stroke of the operated key, two groups ofrecording relays at the central of fice, each group comprising as manyrelays as there are harmonic responsive means and means controlled oversaid line for rendering a relay of the first group responsive to saidresponsive means upon the suppression of one of said hermonies duringthe down-stroke of an operated key'and for thereafter rendering one ormore relays of the second group of relays responsive to said responsivemeans upon the suppression of" one or more of said harmonics during theupstroke of an operated key s 12. The combination-in a telephone systemof a line having a station thereon, a source or alternating current of abase frequency at the central oflice, means for connecting said sourceto saidline to supply current thereto, a harmonic generator at saidstation responsive to current from edv at said station, a plurality ofkeysat said 'station each having a down and an upstroke, meanscontrollable by said keys for selectively suppressing one of saidgenerated harmonics. during thedown-stroke of a key and for selectivelysup-1 pressing one or more of said generatedharmonics, during theup-stroke of theo-perated key, two

groups of recording relays at, thecentral office,

each. groupcomprising asv many relays as there are harmonic responsivemeans, means controlled,-

the suppression of one of said harmonics duringthe down-stroke of anoperated key and for thereafter rendering one or more relays ofthesecond group responsive to saidresponsive means upon the suppression ofone or more 01- said harmonics during the rip-stroke of an operated key,a plurality of registers and means for successive-- ly setting saidregisters'in'accordance with successive joint settings of said groups ofrecording relays. V i e t of said line for generating current ofaplurality of said groups of relays with said responsive means and meanscontrolled over said line for controlling saidtransfer relay forrendering one of said,

groups of relays responsive to said responsive means to register thefirst impulse of a transmitted digit signal and for thereafter renderingthe other of said groups of relays responsive to said responsive meansto register the other impulse of the same digit signal. l

14. In a telephone system, a calling line, a central oflice, means forextending a connectionfrom said line to said ofiice, means at thesubstation of said line for generating current of a plurality ofdifferent voice frequencies, means for transmitting over said line twoimpulses of selected voice frequencies in accordance with any of tendigit values, means at said'central oflice responsive respectively tosaid different voice frequen-' cies, two groups of recording relays,each group comprising as many relays as there are frequency responsivemeans, a first and a second counting relay, means controlled over saidline for operating said first counting relay prior to the trans missionof th first impulse of each digit signal,

for operating said second counting relay during the transmission of saidfirst, impulse, for releasing the first counting relay priorto thetransmission of the second impulse of each digit signal and forreleasing said second counting relay duringthe transmission of saidsecond impulse, a transfer relay for associating either of said groupsof recording relays with said responsive means, an operatingcircuit forsaid transfer relay effective upon the release of said first countingrelay while said second counting relay is still operated and means forreleasing said transfer relay effective upon the subsequent release ofsaid second counting relay and the reoperation of said first countingrelay, whereby one of said groups of relays is rendered responsiv tosaid responsive means to register the first impulse of a transmitteddigit signal and the other of said groups of relays is thereafterrendered responsive to said responsive means to register the otherimpulse of the same digit signal.

' FRANCIS A. HUBBARD.

